repo: Fix blank line issues reported by flake8

Change-Id: I62633e71a36b2acbd09e205447a02159dd334896
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254694
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: David Pursehouse <dpursehouse@collab.net>